Several approaches have been developed for detection of analytes in a biological sample for routine diagnostics in diagnostic laboratories via for instance immunochromatography.
EP 0 088 636, EP 0 186 799, EP 0 284 232 and WO 88/08534 disclose sheet-like chromatographic devices comprising at least a first and a second zone or region. Prior art devices disclosed in these documents comprise:                a first region or zone containing porous active material to allow liquid to move to the sensitized region coated with specific reagents. This first zone or region comprises a detection reagent dried on it or impregnated into it. It may further contain an application (sub)zone and/or an absorption (sub)zone. This first zone is generally referred to as the application zone;        a second region or zone, also referred to as the detection zone, made of porous active material on which specific reagents are adsorbed. Some of these reagents laid down onto a subzone (e.g. a line) of the second region of the device are specific for the analyte to be detected and should react with the sample analyte-labeling reagent complex while other non-specific reagents eventually laid down onto a further subzone (e.g. as a further line) of the second region are dedicated to react with the excess of the detection reagent. This second zone or region, preferably made out of nitrocellulose, may also contain a control subzone, preferably behind the detection zone; and        a third region or zone made of porous material dedicated to absorb excess of liquid coming through the first and second regions. This region is generally referred to as the absorbent or absorption region.        
The (immuno)chromatographic devices of the prior art may have a plastic or other backing support and/or may be comprised in a water-impervious housing.
The three regions are in capillary contact to allow liquid movements from the application zone to the third region.
Although useful, currently available chromatographic devices using test strips have a number of drawbacks. Many samples, such as fecal samples, contain particulate matter that can clog the pores of the chromatographic medium, greatly hindering the immunochromatographic process. In addition it is frequently difficult with existing chromatographic test devices to apply the sample to the chromatographic medium so that the sample front moves uniformly through the chromatographic medium to ensure that the sample reaches the area where binding is to occur in a uniform, straight-line manner.
Sample preparation and waste generation are responsible for other problems with currently available devices and techniques for immunochromatography. It is rarely possible to apply a sample (such as feces) or a sampling device (such as a throat swab) directly to the chromatographic medium. Several extraction and pretreatment reactions are usually required before the sample can be applied to the chromatographic medium. These reactions are typically carried out by the physician or technician performing the test in several small vessels, such as test tubes or microfuge tubes, requiring the use of transfer devices such as pipettes. Each of these devices is then contaminated and must be disposed of using special precautions so that workers or people who may inadvertently come into contact with the waste do not become contaminated.
Therefore, it would be desirable to have a chromatographic assay device capable of receiving a possibly contaminated sample or a sample preparation device directly so as to eliminate the need for extraction vessels and transfer devices. Such a device, preferably in the form of a test strip, should also be capable of performing assays on samples containing particulates without clogging or without interference and should be able to deliver the sample to the chromatographic medium uniformly and evenly to improve accuracy and precision of the test. This aspect of an improved assay device is particularly important in avoiding false negatives and false positives.